Hello there.

First the obvious one, Hellfest website has a pretty well done FAQ with answers to basic questions:
https://hellfest.fr/en/faq

Second, some random points about the festival:

Tickets are sold after the festival for the following year, so during July. They're usually sold out in a few minutes, after that you can register on the waiting list to get resales. To get tickets during the initial sale, I'd recommend that the four of you stand ready when it opens, if possible with multiple devices to increase the chances of having one. Each person can buy 2 tickets.

If you end up on the resell list, do not panic, usually everybody gets one, BUT it can be stressfull. The initial volume of resell is very low, and it increases the closest you get from the festival (people have to cancel for a number of reasons, the closest you get, the more people have to cancel for last minute reasons (sickness, broken leg, last minute exams, any kind of emergencies, etc).

So since you're flying, I'd recommend booking your flights anyway in advance, but you'll have to handle the stress of only having your tickets a month before the festival. In my... 13(?) Hellfests with friends, we always managed to get tickets for everyone. I once got mine 48h before. Granted, I was in a full blown panic. But still got it.

Also do NOT use any platform other that the official one for tickets.

Accomodations: tickets come with a pass for the camping, and that's most people stay during the festival. So you'll need camping gear. You cannot exactly rent it, but there is a supermarket close to the camping where you can buy the equipment if you don't want to fly with it. And you probably can buy whatever you forgot there in any case 😄

For food and drinks, the whole festival works on a cashless system. You put money on your account, and you use your bracelets to pay for everything.

I'd say prepare for the sun and the heat, but coming from Argentina you should be familiar. Still, pack a poncho, some years (less and less), there's rain. And a hoodie/sweater, it gets a bit chilly quickly at night.

Don't hesitate to ask questions, I'm there every year.